This invention relates generally to an electrophptographic copying apparatus, and, more particularly, to the heat and pressure fixing of toner images formed on a copy substrate by direct contact with a heated fusing member.
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles commonly referred to as toner. The visual toner image is typically transferred from the member to a copy substrate, such as a sheet of plain paper, with subsequent affixing of the image by one of several fusing techniques. A preferred fusing system applies both heat and pressure to the copy substrate.
In a secured fusing system, a fuser roll is used which has an outer surface or covering of polytetrafluoroethylene or silicone rubber, the former being known by the tradename Teflon, to which a release agent such as silicone oil is applied, the thickness of the Teflon being on the order of several mils and the thickness of the oil being less than 1 micron. Silicone based oils which possesses a relatively low surface energy, have been found to be materials that are suitable for use in a heated fuser roll environment where Teflon constitutes the outer surface of the fuser roll. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to form an interface between the roll surface and the toner images carried on the support material.Thus a low surface energy layer is presented to the toner as it passes through the fuser nip and thereby prevents toner from offsetting to the fuser roll surface. A fuser roll construction of this type is disclosed in U.S. Pat. No. 3,718,116 assigned to Xereox Corporation.
While heat and pressure fusers of the type discussed above, are desirable because of their thermal efficiency, they possess some undesirable because of their mechanical complexity, cost, long warm-up times and paper wrinkling. A third type of system is known in the prior art which reduces or eliminates these undesireable characteristics. This system utilizes a relatively low mass fuser roll member of the type disclosed, for example, in U.S. Pat. No. 4,689,471 assigned to Xerox Corporation. As disclosed in this patent, a low mass heated fuser roll coopertes with an elongated web member comprising a woven fabric to form an extended fusing area. One end of the pressure web is fixed while the other end is biased into pressure engagement with the fuser roll forming an entrance nip. The pressure web is an enabling feature of this type of system but the effectiveness depends upon several factors such as the type of copy substrate media being used, and the amount of oil applied to the fuser roll. As one example, the use of high moisture content paper such as tracing paper, tends to create poor fusing conditions because of moisture buildup.
The present invention is, therefore directed to a fusing system utilizing a low mass fuser roll and a pressure web member which is modified to improve the performance of the web with regard to fusing of lightweight or high moisture content copy media. In one embodiment the invention is directed to a heat and pressure fuser apparatus for fixing toner images to copy substrates, the apparatus comprising:
a fuser roll; PA1 means for elevating the temperature of said fuser roll; PA1 a pressure applying member having an elongated surface contacting said fuser roll to form a nip therebetween through which copy substrate pass with toner images carried thereby contacting said fuser roll said member having a conductive surface proximate the fuser roll and; PA1 means for mounting said pressure applying member and for urging substantially the entire surface thereof into pressure engagement with said fuser roll, said pressure applying member comprising a thin web fabricated froma material having a conductive surface proximate the fuser roll.
Further disclosure believed to be material is found U.S. Pat. No. 4,112,280 assigned to Eastman Kodak Company. This patent discloses an apparatus for heat processing a sheet of web material which includes a rotary drum and a guide web of low friction material and an idler web which cooperates with the moving drum to effect feed of the material through the processing path .